Summary of Work: The Avon Longitudinal Study of Pregnancy and Childhood (ALSPAC) is a unique prospective of pregnancy in which 14,000 mother's were enrolled when they first became pregnant and now their children have continued to be followed as they approach school age. We are collaborating with researchers from the ALSPAC study on a study of the effect of having dental work done during pregnancy on subsequent childhood development. In Great Britain, many women receive extra dental care during pregnancy when their insurance coverage is increased. Mercury vapor can cross the placenta but it is not known whether there are any adverse effects on the fetus. Having dental work done during pregnancy could also affect the fetus by spreading infection through the bloodstream. We recently received a data set that we will use to look at the effect of dental treatment during pregnancy on infant development. The data set contains questions on motor and cognitive milestones adapted from the Denver Developmental Screening Test,on temperament and behavior that were adapted from the Carey Infant temperament Questionnaire, and speech and language development adapted from the McCarthur infant communication questionnaire. On about 1500 of the children, we will also have data on the mercury levels in the umbilical cord itself. We looked for predictors of cord mercury levels and using regression models found that fish consumption, having 4 or more amalgams in one's mouth and having dental work done during pregnancy were related to increased cord mercury levels. This is one of the first studies to use cord mercury levels as a marker for mercury vapor exposure (it had been used before as a marker of methyl mercury).